Realistic character emotions
Try Blender's Pose Library. If you create a pose you like manually, you can select the bones that correspond with it and press the "+" button in the Pose Library to create a preset. Now when you want that emotion, all you have to do is go in (select your bones first) and click the magnifying glass icon to assign the pose to a given frame.

Additionally, assuming your various characters use a standardized bone layout/naming system, you should be able to use one library with multiple characters with minimal tweaks.

Please note this does require a lot of manual work on your part to set up initially, so if that defeats the purpose of your question, try looking around for preexisting facial expression pose libraries online. (I would recommend making your own, though, as a third-party library may not use the exact bone/rig naming setup and cause some major issues.)